1. Field of the Invention
The present invention relates to a fuel cell system, and more particularly, to a fuel cell system capable of sensing an electricity output value of a stack in the fuel cell system.
2. Description of the Related Art
A fuel cell system is an electricity generating system which directly converts chemical reaction energy of oxygen and hydrogen contained in a hydrocarbon material such as methanol, ethanol, and natural gas into electrical energy.
The recently developed polymer electrolyte membrane fuel cell (PEMFC) has an excellent output characteristic, a low operating temperature, and fast starting and response characteristics. In addition, the polymer electrolyte fuel cell advantageously has a wide range of applications including a mobile power source for vehicles, a distributed power source for home or buildings, and a small-sized power source for electronic apparatuses.
A fuel cell system employing the PEMFC includes a stack, a reformer, a fuel tank, and a fuel pump. The stack constitutes an electricity generation assembly constructed with a plurality of unit cells, and the fuel pump supplies the fuel of the fuel tank to the reformer. The reformer reforms the fuel to generate a reformed gas containing hydrogen and supplies the reformed gas to the stack.
In the fuel cell system, the fuel pump operates to supply the fuel of the fuel tank to the reformer, and the reformer reforms the fuel to generate the reformed gas. The reformed gas is supplied to the stack, and air is supplied to the stack through a separate air pump. Finally, the stack performs electro-chemical reaction of the reformed gas and oxygen contained in the air to generate electrical energy.
In a fuel cell system employing a direct methanol fuel cell (DMFC), a fuel is directly supplied to a stack without being reformed by a reformer.
In conventional fuel cell systems, electricity output value of the stack is sensed, and the whole system including pumps, auxiliary power supply unit, and the like is controlled according to the electricity output value. Therefore, conventional fuel cell systems typically include a voltage sensor for sensing the electricity output value.
Due to the voltage sensor provided to the conventional fuel cell system, the circuitry and mechanical designs become complicated. According, there is a problem in that the size and power consumption of the system increases.
Particularly, when small-sized mobile apparatus employs such a fuel cell system, the increase in size of the system causes a limitation in the product design of such fuel cell system.